Fix issue #1733: missing key events_summary for jinja template
Fix issue #1733: missing key events_summary for jinja template

For each EmailReporter type currently we should define in class property
the list of jinja template pattern.
New events_summary was missed in list of patterns.

scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests